This invention relates to small containers such as jars and the like, as used for the holding and dispensing of cosmetics, foods, etc., and more particularly to containers constituted mainly of glass, desired for its property of being inert chemically.
The use of wide-mouth jars for holding and dispensing foods, cosmetics, pharmaceuticals, household products and numerous varieties of pastes, ointments, creams, salves and quasi-viscous products is well established. In the past, containers which served this purpose used to be constituted exclusively of flint glass, opal glass, ceramic material and colored soda lime glass. More recently, jar constructions have comprised resinous materials, such as polyethylene, polypropylene, polystyrene, acrylonitriles and polyesters. However, the use of these plastic materials resulted in a limited efficacy in the containing of many products that are sensitive to oxygen and moisture, since no plastic material could offer the barrier to gases and vapors that glass could. Furthermore, highly acidic formulations and those containing hydrocarbon solvents would attack, swell, soften and dissolve many of the plastic resins.
Glass containers have long been recognized for their superior barrier properties and maintenance of product purity and cleanliness. However, they have the drawback of being susceptible to fracture, often into sharp shards, as a consequence of impact, thermal shock, pressures, torsion and internal strains. Glass containers generally follow the physical laws which apply to glass members as a class. A principal rule teaches that glass fails when it is placed in tension, as by outside forces, internal forces, etc., whereas glass stoutly resists failure due to compression forces exerted on it.
In connection with containers, mouth or neck finishes refer to the configurations at the openings, involving the screw threads, lugs, sealing surfaces and sizes. In the case of glass, continuous-thread type finishes, lug-type finishes and special configurations in which a closure turns or clamps onto the neck represent almost exclusively the zones of axial tension or loading. These are the areas which are particularly sensitive to glass manufacturing defects, since they are the first to be formed, and are used in the transfer of the container during the intermediate molding stages and prior to the annealing of the glass.